In global navigation satellite systems (GNSS) such as the global positioning system (GPS) or Galileo, satellites broadcast signals which may be used by a GNSS receiver to determine a position of a GNSS receiver.
In order to determine position, a receiver must first acquire a signal being broadcast from a satellite and then track that signal. In acquisition, the receiver acquires a difference in phase between a signal being broadcast from the satellite and a signal generated at the receiver. This phase difference corresponds to a time taken for the signal to propagate from the satellite to the receiver and thus the position of the receiver with respect to the satellite. Once a signal is acquired, this difference in phase may be tracked.
The acquisition and tracking of signals from four or more satellites and hence the relevant position of the receiver with respect to those satellites, allows a receiver to pinpoint its position. It will of course be appreciated, that in some case, some of the signals acquired and tracked may have terrestrial origins.
In order to acquire the satellite signal, a local signal is generated in order to determine a phase difference with the satellite signal. Any frequency error in the locally generated signal leads to an increase in the time taken to acquire the satellite signal as the receiver has to search not only for a phase difference but also potential frequency differences.
The accuracy of a frequency generator, such as a crystal oscillator, at the receiver may affect the speed and accuracy of the navigation system.